1. Field of the Invention
The present invention relates to a method and apparatus for chamfering side edges and corners of an electronic package, and more particularly, to a method and apparatus for providing a precise self-aligned chamfer on side edges and corners of the electronic package.
2. Discussion of the Related Art
Controlled Collapsed Chip Connector (C4) ball grid array (BGA) multilayer ceramic (MLC) packages are quickly becoming a staple in the electronics packaging industry. The C4 BGA package offers several advantages over its predecessor, the wire bond pin grid array (PGA) package. Most important of the advantages of the C4 BGA package is its ability to pack more input/output (I/O) into a smaller area. The C4 BGA substrates are normally under 32 mm in size and on the order of 5-7 layers thick (approximately 1.0 mm thick). In comparison, a typical wirebond PGA package would be on the order of 44 or 50 mm in size and about 10 layers thick, thicker than the C4 BGA package.
The smaller size of the ceramic chip carrier presents several problems. One such problem is not having an ability to chamfer both the edges 12 and the corners 14 (FIG. 1) of a ceramic substrate 10 in a reliable and repeatable manner with low loss yields. Corner and edge chamfers are required for both aesthetic reasons as well as for yield purposes. For instance, a sharp ceramic edge is very brittle and vulnerable to chipping and cracking. During semiconductor chip device packaging processes, plating and bond & assembly processes typically fixture off (i.e., reference from) the substrate sides. As a result of fixturing off of the substrate sides, there are usually high yield losses associated with non-chamfered edges. The problem is further complicated by tighter spacings between the substrate side and the active metallurgy of the package which results in less room for the chamfer. A normal BGA chamfer is on the order of 0.004"-0.008" on a side edge and on the order of 0.012"-0.020" at the corners, as compared to 0.006"-0.028" on the side edge and 0.012"-0.025" at the corners for a PGA product. A top surface of the substrate may contain top surface metallurgy (TSM) and/or the bottom surface of the substrate may contain bottom surface metallurgy (BSM) which the chamfer must avoid. FIG. 2 illustrates a substrate 10C having corner and edge chamfers, 14C and 12C, respectively.
The chamfer tools presently used to chamfer PGA product are not suitable for BGA chamfering since the chamfer size which results from use of those tools will vary with the tolerance on the X-Y size and thickness (i.e., as a result of fixed cutter positions). Furthermore, the parts to be chamfered are typically moved, flipped and rotated several times in order to achieve 8 edge chamfers and 4 corner chamfers using such known chamfer tools. Increased handling of a substrate can be a cause for major yield problems in the chamfering of much thinner packages, also.
Finally, since the most cost effective method of producing chamfered substrates is to chamfer the parts in a "green" or unfired state, there is an exposure to the problem of delamination. Delamination is the undesired separating of the layers of the ceramic substrate. The ceramic substrate, in its unfired state, is actually a composite of many layers of ceramic compressed together, wherein the layers tend to separate or delaminate when contacted by a cutting tool.
A chamfering apparatus which overcomes the above problems would be highly desirable in the industry.